crypto/asymmetric_keys/rsa.c

   1 /* RSA asymmetric public-key algorithm [RFC3447]
   2  *
   3  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #define pr_fmt(fmt) "RSA: "fmt
  13 #include <linux/module.h>
  14 #include <linux/kernel.h>
  15 #include <linux/slab.h>
  16 #include "public_key.h"
  17
  18 MODULE_LICENSE("GPL");
  19 MODULE_DESCRIPTION("RSA Public Key Algorithm");
  20
  21 #define kenter(FMT, ...) \
  22         pr_devel("==> %s("FMT")\n", __func__, ##__VA_ARGS__)
  23 #define kleave(FMT, ...) \
  24         pr_devel("<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
  25
  26 /*
  27  * Hash algorithm OIDs plus ASN.1 DER wrappings [RFC4880 sec 5.2.2].
  28  */
  29 static const u8 RSA_digest_info_MD5[] = {
  30         0x30, 0x20, 0x30, 0x0C, 0x06, 0x08,
  31         0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* OID */
  32         0x05, 0x00, 0x04, 0x10
  33 };
  34
  35 static const u8 RSA_digest_info_SHA1[] = {
  36         0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
  37         0x2B, 0x0E, 0x03, 0x02, 0x1A,
  38         0x05, 0x00, 0x04, 0x14
  39 };
  40
  41 static const u8 RSA_digest_info_RIPE_MD_160[] = {
  42         0x30, 0x21, 0x30, 0x09, 0x06, 0x05,
  43         0x2B, 0x24, 0x03, 0x02, 0x01,
  44         0x05, 0x00, 0x04, 0x14
  45 };
  46
  47 static const u8 RSA_digest_info_SHA224[] = {
  48         0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09,
  49         0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04,
  50         0x05, 0x00, 0x04, 0x1C
  51 };
  52
  53 static const u8 RSA_digest_info_SHA256[] = {
  54         0x30, 0x31, 0x30, 0x0d, 0x06, 0x09,
  55         0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01,
  56         0x05, 0x00, 0x04, 0x20
  57 };
  58
  59 static const u8 RSA_digest_info_SHA384[] = {
  60         0x30, 0x41, 0x30, 0x0d, 0x06, 0x09,
  61         0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02,
  62         0x05, 0x00, 0x04, 0x30
  63 };
  64
  65 static const u8 RSA_digest_info_SHA512[] = {
  66         0x30, 0x51, 0x30, 0x0d, 0x06, 0x09,
  67         0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03,
  68         0x05, 0x00, 0x04, 0x40
  69 };
  70
  71 static const struct {
  72         const u8 *data;
  73         size_t size;
  74 } RSA_ASN1_templates[PKEY_HASH__LAST] = {
  75 #define _(X) { RSA_digest_info_##X, sizeof(RSA_digest_info_##X) }
  76         [PKEY_HASH_MD5]         = _(MD5),
  77         [PKEY_HASH_SHA1]        = _(SHA1),
  78         [PKEY_HASH_RIPE_MD_160] = _(RIPE_MD_160),
  79         [PKEY_HASH_SHA256]      = _(SHA256),
  80         [PKEY_HASH_SHA384]      = _(SHA384),
  81         [PKEY_HASH_SHA512]      = _(SHA512),
  82         [PKEY_HASH_SHA224]      = _(SHA224),
  83 #undef _
  84 };
  85
  86 /*
  87  * RSAVP1() function [RFC3447 sec 5.2.2]
  88  */
  89 static int RSAVP1(const struct public_key *key, MPI s, MPI *_m)
  90 {
  91         MPI m;
  92         int ret;
  93
  94         /* (1) Validate 0 <= s < n */
  95         if (mpi_cmp_ui(s, 0) < 0) {
  96                 kleave(" = -EBADMSG [s < 0]");
  97                 return -EBADMSG;
  98         }
  99         if (mpi_cmp(s, key->rsa.n) >= 0) {
 100                 kleave(" = -EBADMSG [s >= n]");
 101                 return -EBADMSG;
 102         }
 103
 104         m = mpi_alloc(0);
 105         if (!m)
 106                 return -ENOMEM;
 107
 108         /* (2) m = s^e mod n */
 109         ret = mpi_powm(m, s, key->rsa.e, key->rsa.n);
 110         if (ret < 0) {
 111                 mpi_free(m);
 112                 return ret;
 113         }
 114
 115         *_m = m;
 116         return 0;
 117 }
 118
 119 /*
 120  * Integer to Octet String conversion [RFC3447 sec 4.1]
 121  */
 122 static int RSA_I2OSP(MPI x, size_t xLen, u8 **_X)
 123 {
 124         unsigned X_size, x_size;
 125         int X_sign;
 126         u8 *X;
 127
 128         /* Make sure the string is the right length.  The number should begin
 129          * with { 0x00, 0x01, ... } so we have to account for 15 leading zero
 130          * bits not being reported by MPI.
 131          */
 132         x_size = mpi_get_nbits(x);
 133         pr_devel("size(x)=%u xLen*8=%zu\n", x_size, xLen * 8);
 134         if (x_size != xLen * 8 - 15)
 135                 return -ERANGE;
 136
 137         X = mpi_get_buffer(x, &X_size, &X_sign);
 138         if (!X)
 139                 return -ENOMEM;
 140         if (X_sign < 0) {
 141                 kfree(X);
 142                 return -EBADMSG;
 143         }
 144         if (X_size != xLen - 1) {
 145                 kfree(X);
 146                 return -EBADMSG;
 147         }
 148
 149         *_X = X;
 150         return 0;
 151 }
 152
 153 /*
 154  * Perform the RSA signature verification.
 155  * @H: Value of hash of data and metadata
 156  * @EM: The computed signature value
 157  * @k: The size of EM (EM[0] is an invalid location but should hold 0x00)
 158  * @hash_size: The size of H
 159  * @asn1_template: The DigestInfo ASN.1 template
 160  * @asn1_size: Size of asm1_template[]
 161  */
 162 static int RSA_verify(const u8 *H, const u8 *EM, size_t k, size_t hash_size,
 163                       const u8 *asn1_template, size_t asn1_size)
 164 {
 165         unsigned PS_end, T_offset, i;
 166
 167         kenter(",,%zu,%zu,%zu", k, hash_size, asn1_size);
 168
 169         if (k < 2 + 1 + asn1_size + hash_size)
 170                 return -EBADMSG;
 171
 172         /* Decode the EMSA-PKCS1-v1_5 */
 173         if (EM[1] != 0x01) {
 174                 kleave(" = -EBADMSG [EM[1] == %02u]", EM[1]);
 175                 return -EBADMSG;
 176         }
 177
 178         T_offset = k - (asn1_size + hash_size);
 179         PS_end = T_offset - 1;
 180         if (EM[PS_end] != 0x00) {
 181                 kleave(" = -EBADMSG [EM[T-1] == %02u]", EM[PS_end]);
 182                 return -EBADMSG;
 183         }
 184
 185         for (i = 2; i < PS_end; i++) {
 186                 if (EM[i] != 0xff) {
 187                         kleave(" = -EBADMSG [EM[PS%x] == %02u]", i - 2, EM[i]);
 188                         return -EBADMSG;
 189                 }
 190         }
 191
 192         if (memcmp(asn1_template, EM + T_offset, asn1_size) != 0) {
 193                 kleave(" = -EBADMSG [EM[T] ASN.1 mismatch]");
 194                 return -EBADMSG;
 195         }
 196
 197         if (memcmp(H, EM + T_offset + asn1_size, hash_size) != 0) {
 198                 kleave(" = -EKEYREJECTED [EM[T] hash mismatch]");
 199                 return -EKEYREJECTED;
 200         }
 201
 202         kleave(" = 0");
 203         return 0;
 204 }
 205
 206 /*
 207  * Perform the verification step [RFC3447 sec 8.2.2].
 208  */
 209 static int RSA_verify_signature(const struct public_key *key,
 210                                 const struct public_key_signature *sig)
 211 {
 212         size_t tsize;
 213         int ret;
 214
 215         /* Variables as per RFC3447 sec 8.2.2 */
 216         const u8 *H = sig->digest;
 217         u8 *EM = NULL;
 218         MPI m = NULL;
 219         size_t k;
 220
 221         kenter("");
 222
 223         if (!RSA_ASN1_templates[sig->pkey_hash_algo].data)
 224                 return -ENOTSUPP;
 225
 226         /* (1) Check the signature size against the public key modulus size */
 227         k = mpi_get_nbits(key->rsa.n);
 228         tsize = mpi_get_nbits(sig->rsa.s);
 229
 230         /* According to RFC 4880 sec 3.2, length of MPI is computed starting
 231          * from most significant bit.  So the RFC 3447 sec 8.2.2 size check
 232          * must be relaxed to conform with shorter signatures - so we fail here
 233          * only if signature length is longer than modulus size.
 234          */
 235         pr_devel("step 1: k=%zu size(S)=%zu\n", k, tsize);
 236         if (k < tsize) {
 237                 ret = -EBADMSG;
 238                 goto error;
 239         }
 240
 241         /* Round up and convert to octets */
 242         k = (k + 7) / 8;
 243
 244         /* (2b) Apply the RSAVP1 verification primitive to the public key */
 245         ret = RSAVP1(key, sig->rsa.s, &m);
 246         if (ret < 0)
 247                 goto error;
 248
 249         /* (2c) Convert the message representative (m) to an encoded message
 250          *      (EM) of length k octets.
 251          *
 252          *      NOTE!  The leading zero byte is suppressed by MPI, so we pass a
 253          *      pointer to the _preceding_ byte to RSA_verify()!
 254          */
 255         ret = RSA_I2OSP(m, k, &EM);
 256         if (ret < 0)
 257                 goto error;
 258
 259         ret = RSA_verify(H, EM - 1, k, sig->digest_size,
 260                          RSA_ASN1_templates[sig->pkey_hash_algo].data,
 261                          RSA_ASN1_templates[sig->pkey_hash_algo].size);
 262
 263 error:
 264         kfree(EM);
 265         mpi_free(m);
 266         kleave(" = %d", ret);
 267         return ret;
 268 }
 269
 270 const struct public_key_algorithm RSA_public_key_algorithm = {
 271         .name           = "RSA",
 272         .n_pub_mpi      = 2,
 273         .n_sec_mpi      = 3,
 274         .n_sig_mpi      = 1,
 275         .verify_signature = RSA_verify_signature,
 276 };
 277 EXPORT_SYMBOL_GPL(RSA_public_key_algorithm);